The problem of back-to-front cancellation in acoustic devices, such as loudspeakers, has long been known. Such cancellation is due to sound waves produced by the back of the loudspeaker diaphragm destructively interfering with sound waves produced by the front of the loudspeaker diaphragm. The problem is particularly prominent at low (bass) frequencies. One way of reducing the effects of this problem is to house the loudspeaker in an enclosure, thereby containing the interfering sound waves produced by the back of the loudspeaker diaphragm. However, this solution presents problems. One such problem is that gas within the enclosure impedes the movement of the loudspeaker diaphragm. Not only does this reduce the efficiency of the loudspeaker, but also it can negatively affect the bass performance of the loudspeaker. The resonant frequency of a loudspeaker unit is dependent on the moving mass of the driver, and the combination of the impedance to diaphragm movement both due to the air in the enclosure and due to the suspension of the loudspeaker. The impedance of the combination is higher than either impedance individually. Consequently, the resonant frequency of the loudspeaker unit is increased (and the bass performance is decreased) when a loudspeaker is enclosed. One way to reduce the impedance of the air in the enclosure (and thus improve the bass performance of the loudspeaker) is to enlarge the enclosure, for example by introducing a cavity. However, this is particularly undesirable when manufacturing loudspeakers for mobile devices such as mobile phones, PDAs, laptops and the like.